1. Technical Field
The present invention relates to a method of reducing emissions in the exhaust gases of an internal combustion engine. More specifically, the invention relates to a method of reducing emissions in an internal combustion engine having at least one cylinder to which an air/fuel mixture is supplied when a crankshaft of the internal combustion engine rotates, at least one intake valve, at least one exhaust valve, and a piston reciprocating between a top dead-center position and a bottom dead-center position in the cylinder.
2. Background Information
In internal combustion engines, it is desirable to reduce substances or emissions present in the exhaust gases of the engine in order to reduce pollution of the surrounding environment as well as satisfy legal requirements for internal combustion engines. Emissions present in the exhaust gases include, inter alia, carbon monoxide (xe2x80x9cCOxe2x80x9d), hydrocarbon compounds (xe2x80x9cHCxe2x80x9d) and nitrogen oxides (xe2x80x9cNOXxe2x80x9d).
In order to reduce these emissions in the exhaust gases, the internal combustion engine is provided with a catalytic converter that, by means of a chemical reaction, burns these undesirable emissions completely. The chemical reaction in the catalytic converter occurs only when the catalytic converter has reached a predetermined working temperature. This temperature is reached after a predetermined operating time of the internal combustion engine. When the engine is cold-started, there is therefore no reduction of these undesirable emissions in the catalytic converter.
There are known arrangements that heat the catalytic converter when the internal combustion engine is cold-started. This is done in order to rapidly reach a desirable working temperature of the catalytic converter, thereby making it possible to reduce the undesirable emissions in the exhaust gases of the internal combustion engine at an early stage. In one such known arrangement, an electric heating element is arranged in the catalytic converter. However, this arrangement makes the catalytic converter complicated and expensive to produce.
Another problem that arises when internal combustion engines are cold-started is that a comparatively great amount of fuel in relation to the air supplied, or a rich air/fuel mixture, has to be supplied to the internal combustion engine in order to start the internal combustion engine, and in order to have the internal combustion working at an essentially constant speed while running at idle. This rich air/fuel mixture is also supplied so that the engine will be ready to provide increased torque when the accelerator is operated. By supplying this rich air/fuel mixture, the ability of the internal combustion engine to operate is ensured before the internal combustion engine has reached its operating temperature.
Without any emission control in the catalytic converter, the rich air/fuel mixture results in the CO, HC and NOx content emitted from the internal combustion engine being high when the internal combustion engine is cold-started.
Attempts have previously been made to reduce the quantity of fuel in relation to the air supplied, i.e., run the internal combustion engine with a leaner air/fuel mixture when the internal combustion engine is cold-started. However, this has resulted in the internal combustion engine working very unevenly when idling, and also poor operation of the internal combustion engine.
The reason why the speed varies while idling is that the torque generated by the internal combustion engine is very sensitive to variations in the lambda value of the air/fuel mixture supplied to the cylinder space of the internal combustion engine when the air/fuel mixture is lean. The lambda value, or excess air factor as it is also known, is the actual air quantity supplied divided by the air quantity theoretically necessary for complete combustion. If the lambda value is greater than 1, the air/fuel mixture is lean. If the lambda value is less than one, the air/fuel mixture is rich.
The fuel supplied by a fuel injection valve can be controlled accurately by means of the internal combustion engine fuel injection system in order to obtain a substantially constant lambda value for the air/fuel mixture supplied. However, when the internal combustion engine is cold, fuel condenses on the comparatively cold walls of the intake duct and the cylinder. The fuel condensed on the walls vaporizes during idling and accompanies the air/fuel mixture flowing in the intake duct and being supplied to the cylinder space. If vaporization of the fuel condensed on the walls is uneven, e.g., on account of pressure variations, temperature gradients, or the flow rate of the air/fuel mixture in the intake duct, a variation in the lambda value of the air/fuel mixture supplied to the cylinder space occurs.
Since torque generated by the internal combustion engine varies during idling when cold-started, the internal combustion engine speed varies. In this regard, the internal combustion engine speed refers to the speed of rotation of the internal combustion engine crankshaft. When the speed varies, the pressure in the intake duct will also vary. This, in turn, leads to vaporization of the condensed fuel varying so that a variation of the lambda value of the air/fuel mixture supplied to the cylinder space occurs. In doing so, the uneven speed of the internal combustion engine is intensified.
Accordingly, there is a need for reducing emissions in the exhaust gases of an internal combustion engine during cold-starting of the engine. Further, there is a need for enabling an internal combustion engine to work with a lean air/fuel mixture.
The present invention provides a method of reducing carbon monoxide, hydrocarbon compounds and nitrogen oxides in exhaust gases from an internal combustion engine when cold-started. The invention also makes it possible for an internal combustion engine to work with a lean air/fuel mixture. Further, the invention provides a method for reaching the working temperature of the catalytic converter as rapidly as possible.
This is achieved by a method that includes the steps of supplying an air/fuel mixture with a lambda value greater than 1 to the cylinder, maintaining a substantially constant predetermined speed of the crankshaft by means of an electric motor/generator connected to the crankshaft, and controlling the exhaust valve so that it opens before the piston has passed the bottom dead-center position.
By supplying an air/fuel mixture greater than 1 to the cylinder, undesirable emissions in the exhaust gases emitted from the internal combustion engine are reduced. With the combined electric motor/generator, the internal combustion engine works at a substantially constant speed during idling. By controlling the exhaust valve so that it opens before the piston has passed the bottom dead-center position, the expansion stroke of the piston in the cylinder is interrupted, allowing very hot gases to flow out through the exhaust duct and on to the catalytic converter, thereby rapidly heating the converter.